Fix next_occurrence function

data_safe_haven/functions/strings.py

@@ -46,8 +46,14 @@ def next_occurrence(
             minute=minute,
             second=0,
             microsecond=0,
-        ) + datetime.timedelta(days=1)
+        )
         utc_dt = local_dt.astimezone(pytz.utc)
+        # Add one day until this datetime is at least 1 hour in the future.
+        # This ensures that any Azure functions which depend on this datetime being in
+        # the future should treat it as valid.
+        utc_near_future = datetime.datetime.now(pytz.utc) + datetime.timedelta(hours=1)
+        while utc_dt < utc_near_future:
+            utc_dt += datetime.timedelta(days=1)
         if time_format == "iso":
             return utc_dt.isoformat()
         elif time_format == "iso_minute":

pyproject.toml

@@ -114,6 +114,7 @@ all = [
 [tool.hatch.envs.test]
 dependencies = [
   "coverage>=7.5.1",
+  "freezegun>=1.5",
   "pytest>=8.1",
   "pytest-mock>=3.14",
 ]

tests/functions/test_strings.py

@@ -1,56 +1,59 @@
-import datetime
-import re
-
 import pytest
-import pytz
+from freezegun import freeze_time
 
 from data_safe_haven.exceptions import DataSafeHavenInputError
 from data_safe_haven.functions import next_occurrence, sanitise_sre_name
 
 
-def test_next_occurrence_is_within_next_day():
-    next_time = next_occurrence(5, 13, "Australia/Perth")
-    dt_next_time = datetime.datetime.fromisoformat(next_time)
-    dt_utc_now = datetime.datetime.now(datetime.UTC)
-    assert dt_next_time > dt_utc_now
-    assert dt_next_time < dt_utc_now + datetime.timedelta(days=1)
-
-
-def test_next_occurrence_has_correct_time():
-    next_time = next_occurrence(5, 13, "Australia/Perth")
-    dt_as_utc = datetime.datetime.fromisoformat(next_time)
-    dt_as_local = dt_as_utc.astimezone(pytz.timezone("Australia/Perth"))
-    assert dt_as_local.hour == 5
-    assert dt_as_local.minute == 13
-
-
-def test_next_occurrence_timeformat():
-    next_time = next_occurrence(5, 13, "Australia/Perth", time_format="iso_minute")
-    assert re.match(r"\d\d\d\d-\d\d-\d\d \d\d:13", next_time)
-
-
-def test_next_occurrence_invalid_hour():
-    with pytest.raises(DataSafeHavenInputError) as exc_info:
-        next_occurrence(99, 13, "Europe/London")
-    assert exc_info.match(r"Time '99:13' was not recognised.")
-
-
-def test_next_occurrence_invalid_minute():
-    with pytest.raises(DataSafeHavenInputError) as exc_info:
-        next_occurrence(5, 99, "Europe/London")
-    assert exc_info.match(r"Time '5:99' was not recognised.")
-
-
-def test_next_occurrence_invalid_timezone():
-    with pytest.raises(DataSafeHavenInputError) as exc_info:
-        next_occurrence(5, 13, "Mars/OlympusMons")
-    assert exc_info.match(r"Timezone 'Mars/OlympusMons' was not recognised.")
-
-
-def test_next_occurrence_invalid_timeformat():
-    with pytest.raises(DataSafeHavenInputError) as exc_info:
-        next_occurrence(5, 13, "Australia/Perth", time_format="invalid")
-    assert exc_info.match(r"Time format 'invalid' was not recognised.")
+class TestNextOccurance:
+    @pytest.mark.parametrize(
+        "hour,minute,timezone,expected",
+        [
+            (5, 13, "Australia/Perth", "2024-01-02T21:13:00+00:00"),
+            (0, 13, "Australia/Perth", "2024-01-02T16:13:00+00:00"),
+            (20, 13, "Australia/Perth", "2024-01-02T12:13:00+00:00"),
+            (20, 13, "Europe/London", "2024-01-02T20:13:00+00:00"),
+        ],
+    )
+    @freeze_time("1am on Jan 2nd, 2024")
+    def test_next_occurrence(self, hour, minute, timezone, expected):
+        next_time = next_occurrence(hour, minute, timezone)
+        assert next_time == expected
+
+    @freeze_time("1am on July 2nd, 2024")
+    def test_dst(self):
+        next_time = next_occurrence(13, 5, "Europe/London")
+        assert next_time == "2024-07-02T12:05:00+00:00"
+
+    @freeze_time("1am on Jan 2nd, 2024")
+    def test_timeformat(self):
+        next_time = next_occurrence(5, 13, "Australia/Perth", time_format="iso_minute")
+        assert next_time == "2024-01-02 21:13"
+
+    @freeze_time("9pm on Jan 2nd, 2024")
+    def test_is_tomorrow(self):
+        next_time = next_occurrence(5, 13, "Australia/Perth")
+        assert next_time == "2024-01-03T21:13:00+00:00"
+
+    def test_invalid_hour(self):
+        with pytest.raises(DataSafeHavenInputError) as exc_info:
+            next_occurrence(99, 13, "Europe/London")
+        assert exc_info.match(r"Time '99:13' was not recognised.")
+
+    def test_invalid_minute(self):
+        with pytest.raises(DataSafeHavenInputError) as exc_info:
+            next_occurrence(5, 99, "Europe/London")
+        assert exc_info.match(r"Time '5:99' was not recognised.")
+
+    def test_invalid_timezone(self):
+        with pytest.raises(DataSafeHavenInputError) as exc_info:
+            next_occurrence(5, 13, "Mars/OlympusMons")
+        assert exc_info.match(r"Timezone 'Mars/OlympusMons' was not recognised.")
+
+    def test_invalid_timeformat(self):
+        with pytest.raises(DataSafeHavenInputError) as exc_info:
+            next_occurrence(5, 13, "Australia/Perth", time_format="invalid")
+        assert exc_info.match(r"Time format 'invalid' was not recognised.")
 
 
 @pytest.mark.parametrize(